The present invention relates to an electron gun and an electron beam drawing apparatus using the same and, more particularly, to an electron gun preferably used in a multi-electron beam drawing apparatus capable of realizing high throughput and high precision in the lithography process of a semiconductor device such as a DRAM having a memory capacity of 4 Gbits or more, and an electron beam drawing apparatus using the same.
An electron beam drawing apparatus has conventionally been used to form a mask as an original for a semiconductor device such as a DRAM or MPU. Because of high resolution, such electron beam drawing apparatus is recently applied to an exposure apparatus used in a lithography process among semiconductor manufacturing processes in which the devices are being downsized.
At present, so-called direct drawing type electron beam exposure apparatuses have been developed as apparatuses applicable to design rules for a 4-Gbit DRAM and subsequent DRAMs. This type of electron beam exposure apparatus draws a pattern on a semiconductor substrate by converging an electron beam emitted by an electron gun and controlling the focal position by a deflector, electromagnetic lens, and the like.
However, several problems arise when these apparatuses are applied to the semiconductor device mass production process. The most serious problem is the drawing speed, and these apparatuses must achieve drawing speed as high as several ten to several hundred times of speed of the conventional apparatus to obtain the same throughput of a so-called mask drawing apparatus.
One means for solving this problem is multi-beam type electron beam drawing apparatuses of splitting an electron beam emitted by an electron gun into a plurality of beams, e.g., several thousand beams, arranging them in a matrix, and simultaneously drawing a pattern with the respective electron beams. These apparatuses simultaneously draw a pattern on a wide field of view with a plurality of electron beams, and thus can greatly increase the throughput.
Since a pattern is directly drawn by split electron beams, the luminance must be high to a certain degree as a characteristic required for the electron gun of such apparatus which directly draws a pattern on a substrate using a plurality of electron beams having the same beam intensity over a wider field of view. In addition, since one electron beam is split into a plurality of electron beams over a wide field of view, the angle vs. current distribution of the beam intensity must be flat, and the emittance must be high.
In general, the luminance and emittance are conserved quantities, and their values are determined by the electron gun serving as a light source.
An electron gun used in a conventional electron beam drawing apparatus is basically constituted by a cathode having a projecting or sharpened distal end in order to increase the luminance, a Wehnelt cathode for receiving a potential lower than a voltage applied to the cathode and converging electrons emitted by the cathode, and an anode to which a ground potential is applied.
The triode type electron gun has a simple structure and high operability, and thus is generally widely used. FIG. 4 is a sectional view showing the schematic structure of the main part of a conventional electron gun having a triode structure.
The electron gun in FIG. 4 has a triode coaxial structure made up of a cathode 50 serving as an electron source, Wehnelt cathode 51, and anode 52, and comprises an insulator 53, support electrodes 56 and 57, and heaters 54 and 55. The distal end of the cathode 50 is sharp in order to concentrate an electric field on a small region, and has a radius of curvature of about 50 to 100 xcexcm.
The cathode 50 is heated by so-called energization heating of flowing a current through the heaters 54 and 55 via the support electrodes 56 and 57. In order to accelerate electrons emitted by the cathode 50 to a predetermined energy, the anode 52 receives a voltage higher than the cathode potential by about 10 to 50 kV.
In practice, the anode 52 is grounded, so that a high negative voltage is applied to the support electrodes 56 and 57 of the cathode 50 via bias resistors 58 and 59. The potential of the Wehnelt cathode 51 is much lower than the cathode potential by about 100 to 1,000 V. This potential limits an electron current emitted by the cathode 50, and the Wehnelt cathode 51 operates as a lens having a convergent effect to form a crossover 60.
FIG. 5 shows an angle vs. current distribution 101 of this electron gun. In this example, the current density is about 2xc3x97106, and the crossover radius is about 5 xcexcm.
In general, the luminance and emittance of this electron gun are up to 10 6A/cm2/str and up to 50 xcexcmxc2x7mrad, respectively.
In the conventional electron gun, the emittance decreases as the luminance increases, and the luminance decreases as the emittance increases. The emittance cannot be increased, while the luminance is kept high to a given degree.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide an electron gun capable of emitting an electron beam with a flat angle vs. current distribution and a uniform intensity distribution over a wide field of view while keeping relatively high luminance, and to provide various electron beam application apparatuses using the electron gun and, more particularly, an electron beam drawing apparatus having high throughput.
To achieve the above object, an electron gun according to the present invention comprises a cathode having a hemispherical electron-emitting surface, an anode which is arranged to face the cathode, and has a first aperture on an optical axis, and a bias electrode which is arranged between the anode and the cathode, and has on the optical axis a second aperture having a radius larger than a radius of the electron-emitting surface of the cathode, wherein a distal end of the electron-emitting surface of the cathode is arranged in contact with or outside a virtual sphere whose diameter is equal to the diameter of the second aperture of the bias electrode.
In this manner, according to the present invention, electrons are emitted by the hemispherical electron-emitting surface, and the cathode is arranged on or outside the sphere whose diameter is equal to the inner diameter of the bias electrode. Accordingly, the present invention can provide an electron gun which forms an electrostatic lens exhibiting a flat angle vs. current distribution on a crossover, and has high luminance and high emittance.
The diameter of the second aperture of the bias electrode may be set twice the diameter of the hemispherical electron-emitting surface of the cathode, and electrons may be emitted by the entire hemispherical surface to increase the electron beam intensity.
The radius of the first aperture of the anode may be set smaller than that of the second aperture of the bias electrode to weaken the effect of a concave lens formed by the second aperture and prevent divergence of an electron beam.
A portion of the anode facing the bias electrode may project toward the electron-emitting surface of the cathode to increase the power of an electrostatic lens formed by the bias electrode. Consequently, the present invention can provide an electron gun having a flatter angle vs. current distribution.
An electron beam drawing apparatus according to the present invention comprises an electron gun, a substrate stage, and a projection system arranged between the electron gun and the substrate stage, the electron gun having a cathode having a hemispherical electron-emitting surface, an anode which is arranged to face the cathode, and has a first aperture on an optical axis, and a bias electrode which is arranged between the anode and the cathode, and has on the optical axis a second aperture having a radius larger than a radius of the electron-emitting surface of the cathode, wherein a distal end of the electron-emitting surface of the cathode is arranged in contact with or outside a virtual sphere whose diameter is equal to the diameter of the second aperture of the bias electrode.
In this way, the electron gun having high luminance and high emittance can be applied to various electron beam application apparatuses.
A device manufacturing method according to the present invention comprises the steps of applying a photosensitive agent to a substrate, drawing a pattern on the substrate by a charged-particle beam drawing apparatus, and performing developing processing to the substrate, wherein the charged-particle beam drawing apparatus is an electron beam drawing apparatus having an electron gun, a substrate stage, and a projection system arranged between the electron gun and the substrate stage, the electron gun having a cathode having a hemispherical electron-emitting surface, an anode which is arranged to face the cathode, and has a first aperture on an optical axis, and a bias electrode which is arranged between the anode and the cathode, and has on the optical axis a second aperture having a radius larger than a radius of the electron-emitting surface of the cathode, and a distal end of the electron-emitting surface of the cathode is arranged in contact with or outside a virtual sphere whose diameter is equal to the diameter of the second aperture of the bias electrode.
Further objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.